UPLIFT OF THE BOLIVIAN OROCLINE COASTAL AREAS BASED ON GEOMORPHOLOGIC EVOLUTION OF MARINE TERRACES AND ABRASION SURFACES: PRELIMINARY RESULTS

Along most of the Southern Peru and Northern Chilean coasts, discontinuous uplifts are recorded by marine terraces and remnant shorelines. Marine terraces along the South American coast have thus preserved a record of eustatic sea level changes and the uplift history of the coastal area in the Andean forearc. One approach to study the tectonic history of the Andean forearc and coastal ranges is to identify the effect it has had on marine sedimentation or erosion patterns along the coastal area. To investigate these processes, the Neogene marine formations are studied in various coastal sections both in southern Peru (Chala and San Juan de Marcona bays) and in northern Chile (from Tongoy to Los Vilos). We chose various sampling sites from each branch of the Arica bend along the coastal area in order to record the different time spans during the Neogene and also the variations in the response of the continental plate to the subduction process along the strike of the margin. Various studies were already undertaken on such problems in both Peru and Chile ,which have mainly lead to the indentification of the last major maximum interglacial (isotopic stage 5). Either abrasion surfaces or succession of marine terraces are studied in order to determine which marker is the most suitable for for collecting chronological data. Differential GPS and cosmogenic dating methods are pursued in order to propose robust ages on these sites thereby enabling us to subtract the effects of local eustatic sea-level changes and identify tectonic uplift.